Will a computed tomography (CT) head scan show midline shift or brain herniation in a patient with suspected severe traumatic brain injury, stroke, or other conditions causing significant brain swelling?

CT Head Reliably Detects Midline Shift and Brain Herniation

Yes, CT head is highly sensitive and the standard imaging modality for detecting midline shift and brain herniation, making it the essential first-line diagnostic test for these life-threatening conditions. 1

Why CT Head is the Gold Standard

Non-contrast CT (NCCT) is specifically designed to detect cerebral edema, swelling, and signs of herniation with excellent sensitivity. 1 The American College of Radiology and multiple neurosurgical societies consistently recommend CT as the primary imaging modality because it:

• Rapidly identifies clinically significant midline shift (≥5 mm), which predicts neurological deterioration and need for urgent neurosurgical intervention 1
• Detects all major herniation patterns including subfalcine, uncal, and cerebellar tonsillar herniation 1
• Visualizes mass effect indicators including compression of basal cisterns, ventricular compression, and shift of the septum pellucidum and pineal gland 1

Specific CT Findings That Indicate Mass Effect and Herniation

Early Warning Signs on CT:

• Frank hypodensity within the first 6 hours and involvement of one-third or more of the MCA territory predict cerebral edema development 1
• Compression of the frontal horn, shift of the septum pellucidum, and later shift of the pineal gland indicate progressive mass effect at risk for herniation 1
• Effacement or complete obliteration of basal cisterns signals dangerous mass effect requiring urgent intervention 1

Quantifiable Thresholds:

• Midline shift ≥5 mm is considered clinically significant and requires neurosurgical consultation 1, 2
• Computer-aided detection algorithms demonstrate 98% sensitivity for detecting acute intracranial hemorrhage and clinically significant midline shift 2

Clinical Context: When Herniation Risk is Highest

Brain herniation typically develops in specific high-risk scenarios:

• Large territorial MCA infarctions that swell within 24 hours ("malignant" brain swelling) causing rapid deterioration 1
• Cerebellar infarctions with swelling, which may cause sudden apnea from brainstem compression 1
• Traumatic brain injury with intracranial hemorrhage, particularly subdural or epidural hematomas 1
• Subarachnoid hemorrhage, where even patients with normal neurologic examinations may have herniation (4% prevalence) or midline shift (5% prevalence) 3

Critical Pitfall to Avoid

Never assume a normal neurologic examination excludes herniation or midline shift. In a study of 78 patients with subarachnoid hemorrhage and completely normal neurologic examinations, 5% had midline shift and 4% had brain herniation on CT, with most cases missed on initial clinical assessment. 3 This underscores why CT imaging before lumbar puncture is mandatory even in neurologically intact patients with suspected intracranial pathology. 1, 3

Serial CT Monitoring

Serial CT scans are essential for monitoring progression of mass effect in high-risk patients:

• Patients with large territorial infarctions require repeat CT within the first 2 days to identify those developing symptomatic swelling 1
• Lateral ventricular volume asymmetry on admission CT (ratio >1.67) predicts subsequent midline shift development with 73% sensitivity and specificity 4
• CT findings guide timing of decompressive craniectomy, which must be performed before irreversible herniation occurs 1

When CT May Be Insufficient

While CT excels at detecting mass effect and herniation, MRI is superior for detecting the underlying ischemic injury in the first 6 hours when CT may appear normal despite large infarct core. 1, 5 However, for the specific question of detecting midline shift or herniation once it has developed, CT remains the definitive imaging modality with rapid acquisition time critical for emergency decision-making. 1